Long-term goal of the proposed research is to establish a non-invasive real-time clinical capability for early detection, diagnosis, monitoring and screening of pre-malignant and malignant lesions. Based on laser-induced fluorescence (LIF) techniques for characterization of 5-aminolevulinic acid (ALA)- induced protoporphyrin IX (PpIX) fluorescence and of endogenous fluorescence, the proposed approach is unique in combining emissions from these 2 types of fluorescence into one maximally informative diagnostic measurement event by utilizing the same excitation wavelength (405nm). Use of topical ALA will minimize procedure duration, side-effects and ensure patient acceptance of this technique. Although this clinical proposal focuses on intra-oral dysplasia and carcinoma, results will translate directly to many other areas of the body. The information gained is also applicable to photodynamic therapeutic modalities. Specific aims: To (l) characterize ALA-induced and endogenous fluorescence in healthy human oral mucosa, dysplasia and squamous cell carcinoma, (2) determine time-based pharmacokinetics of ALA conversion to PpIX in healthy, dysplastic and malignant oral tissue (3) establish a basis for translation of photodynamic data from the hamster model to humans (4) identify effects of co-existing oral pathologies on LIF, (5) evaluate LIF-based differentiation between conditions with a leukoplakic clinical presentation (6) compare diagnostic capability of LIF with conventional measures. Human healthy, premalignant and malignant oral mucosa will be analyzed using low-light level fluorescence cryomicroscopy in biopsies from 60 patients. ALA will be applied as a cream or mouthrinse for 15-90 mins. prior to biopsy. Excitation will occur at 405nm, PpIX detection at 635nm, autofluorescence detection at 470nm. The optimum interval between ALA application and PpIX fluorescence measurement to maximize tumor:healthy tissue fluorescence ratio will be identified. Fluorescence characteristics will be compared with histological status. Fluorescence characteristics of conditions co-existing with dysplasia, carcinoma and of pathologies clinically resembling leukoplakia, carcinoma will be identified. Selectivity, specificity and predictive capability of LIF will be established. This work will provide the basis for non-invasive, real-time, in vivo identification of the need for biopsies, thus minimizing surgical sampling, and permitting early treatment. Fast, non-specialist screening of at risk populations will become possible.